Field of the Invention
At least one example in accordance with the present invention relates generally to DC-AC power inverters.
Discussion of Related Art
The use of power devices, such as uninterruptible power supplies (UPS), to provide regulated, uninterrupted power for sensitive and/or critical loads, such as computer systems and other data processing systems, is known. Known uninterruptible power supplies include on-line UPS's, off-line UPS's, line interactive UPS's, as well as others. On-line UPS's provide conditioned AC power as well as back-up AC power upon interruption of a primary source of AC power. Off-line UPS's typically do not provide conditioning of input AC power, but do provide back-up AC power upon interruption of the primary AC power source. Line interactive UPS's are similar to off-line UPS's in that they switch to battery power when a blackout occurs but also typically include a multi-tap transformer for regulating the output voltage provided by the UPS.
A conventional online UPS rectifies input power provided by an electric utility using a Power Factor Correction circuit (PFC) to provide power to a DC bus. The rectified DC voltage is typically used to charge a battery while mains power is available, as well as to provide power to the DC bus. In the absence of mains power, the battery provides power to the DC bus. From the DC bus, a DC-AC inverter generates an AC output voltage to the load. Since the DC bus is powered either by mains or the battery, the output power of the UPS is uninterrupted if the mains fails and the battery is sufficiently charged. A conventional off-line UPS normally connects a load directly to utility power. When utility power is insufficient to power the load, the off-line UPS operates a DC-AC inverter to convert DC power from a backup power source (e.g., a battery) into desired AC power, which is provided to the load.